Explosive-activated plug

ABSTRACT

An explosive-activated plug for sealing the end of a defective tube in a heat exchanger having parts made of a nickel-chromium, heat-resistant alloy, is charged with a detonator and explosive encased by an aluminum sleeve and having compositions which leave only lead-free products of combustion after firing. This keeps the heat exchanger free from lead which tends to promote intergranular corrosion of the nickel-chromium alloy when the heat exchanging medium is pressurized water, and facilitates handling of the charge.

United States Patent 1 1 Ploger et al.

1451 Nov. 18, 1975 1 1 EXPLOSIVE-ACTIVATED PLUG [75} lnventors: Manfred Ploger; Lothar Stieding,

both of Erlangen. Germany [73] Assignce: Siemens Aktiengesellschaft, Munich,

Germany [22] Filed: Aug. 15, 1973 21] Appl. No; 388,754

[30] Foreign Application Priority Data Aug. 25. 1972 German) 2241753 [52] US. Cl. 102/24 R; 29/421 E; 138/89: 138/97 1511 Int. Cl. F4211 3/04; F1611 55/18 [58] Field of Search 1. 138/89, 97, 103; 102/24 R; 29/421 E [56] References Cited UNITED STATES PATENTS 1212.044 8/1940 Ridle}; 102/24 R X 1344.510 10/1967 Kamcishi ct a] 1 4 1 1 1 1 1 29/421 E 3.785.291 1/1974 Bergbauer et ul 11 29/421 E X OTHER PUBLlCATlO NS Pub1.: Military Explosives" Dept. of Army Tech. Manual TM 9-Apr1 1963 (pp. 102-105. 152-159).

PI'UHUI') E.tuminer-Richard C Queisser Ass/smut Eruminer-Daniel M. Yasich Attorney Agent, or l-irmKen 'on 1S; Kenyon Reilly Carr & Chapin 15 71 ABSTRACT 4 Claims, 1 Drawing Figure U.S. Patent Nov. 18, 1975 (I) as 2 ,3 1.1.

as 22 as EXPLOSIVE-ACTIVATED PLUG BACKGROUND OF THE INVENTION A pressurized water-coolant nuclear reactor installation provides useful heat by a water flow through the reactors pressure vessel and one or more heat exchangers of the tubular type. The water-coolant is pressurized to prevent it from boiling and it is passed through the heat exchangers tubes which convert water into steam which can be used for power purposes. The pressurized watercoolant is radioactive to some degree and it must not be permitted to come into contact with the water being converted to steam in the heat exchanger.

For the above reason, the heat exchanger is carefully constructed with its tubes and tube sheet made ofnick el-chromium, heat-resistant alloy, as exemplified by Inconel 600. The tubes are subject to rigid inspections, and if one becomes faulty, the ends of that tube must be plugged to put it safely out of service. The heat exchanger is usually the vertical type with a horizontal tube sheet in which an upstanding nest of U-shaped tubes are installed, the bottom of the heat exchanger's casing being constructed to feed the pressurized watercoolant into the U-shaped tubes at one end of the nest with the coolant exhausting at the other end.

To plug the ends of a faluty tube, explosive-activated plugs are used, an example being disclosed by U.S. Pat. No. 3,590,877, dated July 6, 1971. An improved form of such a plug is disclosed by the Bergbauer et. al. U.S. patent application Ser. No. 253,853, filed May 16, 1972 and issued Jan. I5, 1974 as U.S. Pat. No. 3,785,29l. Among other features, this improved plug has a body made of the same alloy as the tube to be plugged, and having a blind bore extending into the body from its back end and its back end external portion being tapered to assure that that portion of the plug firmly welds to the tubes inside under the force resulting when the explosive is detonated, the exxplosive being positioned within the tapered portion. Also, the necessary detonator and the explosive are encased by non-metallic material, such as molded paper or plastic, to form a cartridge which after the plug body is inserted in the end ofa faulty tube, may be inserted in the bodys blind bore and, after firing, removed so that only the plug remains, welded to the tubes inside.

It has been found that after a heat exchanger having one or more of its tubes thus plugged has been in service for some time, that it is troubled by possible stresscorrosion cracking problems, apparently intergranular in nature. Insertion of the cartridge intto the blind bore of the plug body after the latter was pushed in a tube end, had to be done very carefully to assure positive firing by the detonator, the latter being electrically fired after installation of the cartridge, from a remote safe location. Firing failure, if it occurred, would require manual removal of the cartridge for its inspection, this being hazardous.

SUMMARY OF THE INVENTION The present invention results from a study of the possible intergranular stress-corrosion trouble, and firing failures.

These studies resulted in the discovery that the detonator and explosive compositions were such that their products of combustion contained lead. After firing and removal of the cartridge of an installed plug, apparently some of the lead could remain to contaminate the pressurized water-coolant flow through the heat exchanger tubes. With the pressurized water operating at temperatures in the area of 300C, the lead apparently could initiate the intergranaular stress-corrosion attributable to the possible cracking problem involved by the nickel-chromiun alloy parts of the heat exchanger, the coolant operating under a pressure consistent with maintaining it liquid at the temperatures noted. The alloy particularly involved was lnconel 600.

Concerning the firing failure possibilities, it was ascertained that handling of the cartridge involved possible displacement ofthe relative positions of the detonator and explosive. The cartridge casing of molded paper or plastic was required to transmit the explosive force to the plug body and then permit removal of the cartridge, but improved security of the parts was considered to be desirable.

The present ivention solves the intergranular stresscorrosion trouble possibility by using compositions for both the detonator and the explosive which cannot possibly leave any lead after firing. In particular, the detonator composition is diazodinitrophenol (C H N O and the explosive providing the plug-to-tube welding force is tetryl (C H N O Neither can leave lead deposits.

Furthermore, the cartridge is made more positively reliable concerning firing certainty by encasing both the detonator and the explosvie, each in cyclindrical form, together in a thin aluminum sheath or tube mechanically integrating the two parts, the tube being surrounded by the former molded paper or plastic cartridge casing. Aluminum has been found to be so softly malleable or easily deformable as to not detract appreciably from the explosive force relied on to weld the plug body to the tubes inside, while being mechanically rigid enough to reliably position the tube parts. The molded paper or plastic cartridge casing prevents the aluminum tube itself from welding to the inside of the plug body, the cartridge being as easily removed from the plug body after firing as it was when completely non-metallic in nature.

BRIEF DESCRIPTION OF THE DRAWING An example of the present invention is illustrated in the form of a longitudinal section by the single FIG- URE of the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION Referring to this drawing, the numeral 2 designates the plug with its cartridge 3, the plug body 21 being largely cylindrical but having its back end 22 tapered with an angularity indicated at a of from 2 to 6. The plug body is in this case made of Inconel 600, widely used in the construction of nuclear reactor pressurized water-coolant heat exchangers. Otherwise than for this tapered back end 22, the plug body has a diameter fitting slidably but snugly the inside of the tube T to be plugged. The blind bore is shwon at 23, it extending for substantially the full length of the plug body. The latter has a somewhat sharply tapered front end for ease of initial insertion in the tube to be plugged.

The cartridge 3 is shown inserted in the plug body's blind bore and as being made of the molded paper or plastic, the cartridge having the tail piece 33 facilitating its insertion in the blind bore 23 after the plug body is inserted, it being understood that the plug body would normally be dimensioned to form a force fit with the tubes inside sufficient to keep the plug in position after its initial insertion. The electric detonator wires 41 are shown as leading through the molded cartridge casing from the detonator shown at 44, the explosive charge 45 being located within the tapered back portion of the plug body. The body's tapered portion avoids using a shaped explosive charge, both the detonator 44 and the explosive charge 45 being cylindrical, and therefore easy to fabricate.

The new thin-walled aluminum tube is shown at 46, it being long enough to integrate the detonator and explosive charge mechanically.

As previously described, both the detonator and explosive have compositions leaving only lead-free deposits after firing: the tube 46 is made of aluminum. After firing, the cartridge casing may be removed as easily as was the casing made completely of non-metallic parts, the aluminum tube not welding to the inside of the plug body. After firing, the plug body is welded to the inside of the tube as firmly as ever.

Also, as previously described, the detonator charge 44 is diazodinitrophenol (C,H,N,O,,) and the explosive charge is tetryl (C H N O Neither leave lead deposits.

What is claimed is:

a tube comprising part of a heat exchanger including tube parts made of nickel-chromium, heat-resistant alloy, said plug being made of a corresponding alloy as the nickel chromium alloy and shaped for a snug. slideable insertion in the tube end and having a longitudinally extending blind bore in which is removably positioned a cartridge including a detonator and an explosive, the cartridge including an explosive force-transmitting casing made of non-metallic material; wherein the improvement comprises an aluminum thin walled tubing mechanically integrating both said detonator and explosive, and said detonator and explosive having compositions which after combustion leave only leadfree deposits.

2. The plug of claim 1 in which said thin walled tubing is a thin metal sleeve enclosing the detonator and explosive, said sleeve being inside of said force-transmitting casing made of non-metallic material.

3. The plug of claim 1 in which said detonator is a charge of diazodinitrophenol and said explosive is a charge of tetryl.

4. The plug of claim 2 in which said detonator is a charge of diazodinitrophenol and said explosive is a charge of tetryl. 

1. AN EXPLOSIVE-ACTIVATED PLUG FOR SEALING THE END OF A TUBE COMPRISING PART OF A HEAT EXCHANGER INCLUDING TUBE PARTS MADE OF NICKEL-CHROMIUM, HEAT RESISTANT ALLOY; SAID PLUG BEING MADE OF A CORRESPONDING ALLOY AS THE NCIKERL CHROMIUM ALLOY AND SHAPED FOR A SNUG, SLIDEABLE INSERTION IN THE TUBE END AND HAVING A LONGITUDINALLY EXTENDING BLIND BORE IN WHICH IS REMOVABLY POSITIONED A CARTRIDGE INCLUDING A DETONATOR AND AN EXPLOSIVE, THE CARTRIDGE INCLUDING AN EXPLOSIVE FORCE-TRANSMITTING CAUSING MADE OF NON-METALLIC MATERIAL; WHEREIN THE IMPROVEMENT COMPRISES AND ALUMINUM THIN WALLED TUBING MECHANICALLY INTEGRATING BOTH SAID DETONATOR AND EXPLOSIVE, AND SAID DETONATOR AND EXPLOSIVE HAVING COMPOSITIONS WHICH AFTER COMBUSTION LEAVE ONLY LEAD-FREE DEPOSITS.
 2. The plug of claim 1 in which said thin walled tubing is a thin metal sleeve enclosing the detonator and explosive, said sleeve being inside of said force-transmitting casing made of non-metallic material.
 3. The plug of claim 1 in which said detonator is a charge of diazodinitrophenol and said explosive is a charge of tetryl.
 4. The plug of claim 2 in which said detonator is a charge of diazodinitrophenol and said explosive is a charge of tetryl. 